The measurement of cardiac output and its adequacy to tissue needs are essential for hemodynamic evaluation. In a recent review it was stated that the venous-to-arterial carbon dioxide difference (dPCO2) could be considered a marker of adequacy of venous blood flow to remove the total CO2 produced by the peripheral tissues. Several studies have already shown that dPCO2 and the cardiac index (CI) are inversely correlated in critically ill patients. However, the dPCO2 can be influenced not only by CI, but also by other factors governing CO2 production and CO2 elimination. The aim of this work was to study the behaviour of dPCO2, measured from central venous blood, and its evolution during the early stage of septic shock.

Forty-six patients with septic shock were prospectively included. dPCO2 was calculated by the difference between the arterial PCO2 and the PCO2 from central venous blood. A value of dPCO2 >6 mmHg was considered high. The CI was measured by transpulmonary thermodilution. ScvO2 and serum lactate were obtained. Patients were separated into a normal dPCO2 group and a high dPCO2 group. The results were compared by Student t test or Mann-Whitney test. P < 0.05 was chosen as significance.

dPCO2 patients with septic shock seem to be related principally to CI. dPCO2 might be a marker of tissue perfusion adequacy to patient's metabolism and could be a resuscitation target for management of septic shock patients.